Both the renin-angiotensin-aldosterone system and the autonomic nervous system are capable of profoundly altering both pressure and salt balance. The proposed studies are designed to provide comparative information regarding the relative importance of each of these systems in the regulation of blood pressure in ccnditions of high or low salt intake, in the normotensive and hypertensive animal. The experimental approach will range from studies in the trained, unanesthetized animal to the quantitation of the Na-K-ATPase in identified single, renal tubules. The investigation will include: (A) Blood pressure response of unanesthetized dogs (sodium replete and sodium depleted, normotensive and renovascular hypertensive) following compression of carotid artery loops. (B) Alterations of blood pressure, plasma renin activity and plasma aldosterone to bilateral reversible vagal blockage in trained dogs in varying salt states, and in developing renovascular hypertension. (C) Blood pressure and plasma renin response to renal artery constriction in trained dogs on low, normal and high salt intake. (D) Studies of factors regulating renin release in the isolated, perfused rat kidney. (E) Studies of factors regulating renin release in the isolated afferent arteriole and juxtaglomerular granular cell. (F) Since the final step in the renin-angiotensin-aldosterone control of circulating volume presumably resides in the modulation of ATPase activity by aldosterone, studies of the Na-K-ATPase will be performed in single tubules using the electron probe.